A TV expose showed video footage from a pig farm where
rats were living with the pigs, and carcasses of dead pigs were
left with the living pigs. Apart from the animal welfare issues,
this kind of farming practice raises also human health issues.
Could you please explain what is the chance of getting Trichinosis
and/or Creutzfeld-Jacob disease ("mad cow disease") when consuming
meat from the pigs living in these kind of conditions?

Our concern is raised by the following facts:
1. Trichinosis: A typical life cycle for T spiralis involves humans, pigs and rodents.
2. Cannibalism among farm animals may be related to Creutzfeldt-Jacob disease
(mad cow disease), and in pigs Trichinosis.

Callum Irvine and Bruce Welch, veterinarians with the New Zealand Veterinary
Association, responded.

CJD is not believed to be present in New Zealand and even in countries where
it exists it has not been associated with pigs.

Trichinosis has been diagnosed in New Zealand but there have been very
few cases in recent decades. Recent surveys done in both the North and
South Island in commercial pig farms producing exported pork did not find
the parasite to be present. In NZ it is thought to be associated with some
wildlife species and possibly in smaller "para-commercial" pig farms.
Commercial farms don’t provide an ideal mechanism for the parasite to
establish and perpetuate itself.

Rats could infect pigs if the pigs ate infected rats (unusual - pigs fed
ad-lib have a much feed as they require) or if they ate rat faeces, although
the latter route of transmission is not as likely as rat faeces are only
infective for a short time after they get infected with Trichinella. Also
the rats themselves would have to become infected with Trichinella which
can't happen on a negative(not infected) farm and doesn’t happen easily where pigs are
positive (infected). All farms have rodent populations varying from very small to
large, but despite that Trichinella still hasn’t been found in commercial
pig farms in recent times. Thus while we couldn’t say there is no risk we
would say the risk was small, and if pork from an infected farm was cooked
adequately the risk to consumers would be removed.

For a person to become infected with Trichinella the following would have to
occur :-

2. Rats become infected with Trichinella from eating dead pigs (would have
to entail poor housekeeping on the farm) which then in turn infect the pigs,
or else pigs pass it between each other which doesn’t happen easily.

3. The pork from infected pigs is eaten without being cooked properly.

New Zealand's health system is good and would be likely to diagnose human
cases of Trichinella if they occurred here. We can’t say that there's no risk
but the risk is certainly small. That doesn’t decrease the importance of
good rodent control on all farms